Chair back



FIG. 1 is a front view of a chair back showing my new design;

FIG. 2 is a back view of a chair back;

FIG. 3 is a left side view of a chair back;

FIG. 4 is a right side view of a chair back;

FIG. 5 is a top view of a chair back;

FIG. 6 is an upward view of a chair back; and,

FIG. 7 is a perspective view of a chair back. 

CLAIM The ornamental design for chair back, as shown and described. 